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Early vocal behaviour and interpersonal arousal coupling

Recently I’ve been working on a few papers looking in our naturalistic data at the relationship between vocal communication and autonomic arousal in infant-caregiver dyads. Why? Because I’ve been thinking that in order to understand self-regulation we can’t just think about how effectively a child manages their own arousal. We need also to think about the child’s emotional communication. This is because most tests of self-regulation look at the child’s overt emotional displays – which presumably are influenced both by what the child is genuinely experiencing, *and* what they’ve learnt is useful to communicate.

So in this paper we looked at how spontaneously occurring vocalisations in 12-month-old infants during the day co-occur with fluctuations in autonomic arousal – both the infant themselves and their primary caregiver. We were building on some fantastic animal work Yisi Zhang and Asif Ghazanfar, which suggests that both infant and adult monkeys are more likely to vocalise around peaks in their own arousal. We were interested to test whether the same patterns could also been seen in humans, for whom it has argued that one crucial differentiator of human language is its functional flexibility – the idea that one vocalisation can stand for different things in different contexts. So we wanted to look at whether early infant vocalisations, and, in particular, early speech-like sounds, are as inflexibly linked to arousal fluctuations as monkey vocalisations are.

To test this we looked at changes in autonomic arousal (heart rate, heart rate variability, and movement) around spontaneously occurring infant and caregiver vocalisations, recorded in home settings during the day. We hand-coded all of the vocalisations we recorded, to split infant vocalisations into cries and speech-like vocalisations.

Our results suggested that the link between arousal and vocalisation likelihood is strong in infants but much weaker in adults – so much so in fact that the infant’s arousal was in fact more predictive of the caregiver’s vocalisations than the caregiver’s own arousal was. We also found a functional dissociation between infants’ speech-like vocalisations and cries: cries are more likely to lead to changes in the caregiver’s arousal, while speech-like vocalisations are more likely to associate with sustained increases in infant arousal, as well as an increase in vocalisations in both infants and caregivers.

These results suggest that caregivers’ differential responses to specific types of vocalisations (i.e., speech-like vocalisations), which are not yet produced flexibly by infants, are an important factor driving speech development, and they suggest that this bidirectional physiological process supports progressively specialised vocalisations through parental selection.

Full paper here.

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